This one is a bit more traditional and savory. In this dish, each vegetable beautifully complements the other. Serve as a vegetarian entree or as an accompaniment to grilled meats. Saute the onion in olive oil in a 2-quart saucepan. Meanwhile, peel the chayotes (chayote has a very thin skin and is easy to peel with a swivel-blade peeler), then cut each in half, scoop out and discard the seed, and dice the flesh. Add to the saucepan, along with the diced chilies, corn, salt, pepper and milk. Cover, and simmer gently for about 15 minutes, or until chayote is tender. Stir in the Parmesan and cook a few seconds until the sauce thickens. Transfer to a serving bowl and sprinkle with cheddar cheese and chili powder. Serves 4.